Silent chains are widely used as timing chains in automobile engines, for transmitting power from the engine crankshaft to one or more valve-operating camshafts. The silent chain is composed of link plates each having a pair of teeth, and in this application, power is transmitted by engagement of either the inner flanks or the outer flanks of the teeth of the link plates with sprocket teeth.
In a conventional silent chain transmission, the tooth form of the link teeth is uniform, as is the tooth form of the sprocket teeth. However, in a conventional silent chain transmission, engagement sounds are generated when pairs of link teeth of the link plates engage with tooth surfaces of the sprocket teeth. Repetition of substantially the same noises causes resonant vibration of the engine at certain engine speeds, and results in an increased noise level.
Various measures have been taken to decrease the noise generated by a silent chain transmission. For example, in a silent chain transmission described in U.S. Pat. No. 6,663,522, a random arrangement type silent chain is utilized, in which first link plates, which seat on a sprocket tooth by engagement of their inner flanks with the sprocket tooth, and second link plates, which seat on a sprocket tooth with their outer flanks engaged with the sprocket tooth, are disposed in a random arrangement along the length of the chain. The mixing ratio of the first link plates to all the link plates is 50% or less, and at least one or more of the second link plates is disposed at front and rear positions relative to each first link plate.
However, since the random arrangement type silent chain disclosed in U.S. Pat. No. 6,663,522 uses first link plate and second link plates having different shapes, manufacture and assembly of the chain is costly and disadvantageous.
An object of the invention is to provide a less expensive silent chain transmission, which exhibits reduced engagement noise.